U.S. patent number 8,795,358 [Application Number 12/529,243] was granted by the patent office on 2014-08-05 for accommodative ocular implant.
This patent grant is currently assigned to Centre National de la Recherche Scientifique--CNRS, Francois Michel. The grantee listed for this patent is Jean-Marc Buisine, Francois Michel. Invention is credited to Jean-Marc Buisine, Francois Michel.
United States Patent |
8,795,358 |
Michel , et al. |
August 5, 2014 |
Accommodative ocular implant
Abstract
The invention relates to a device (1) for the vision correction
of an eye (6), comprising: a converter (3, 3A, 3B, 5A, 5B) which
can generate an electrical and/or magnetic and/or electromagnetic
signal in response to the mechanical energy generated by a movement
of the eye; and a soft lens (2) intended to be aligned with the
eye. The converter is positioned in relation to the lens such that
the electrical and/or magnetic and/or electromagnetic signal
generated during the movement of the eye causes the optical
properties of the lens to change. The invention is characterised in
that the lens (2) includes a polymer material (7) containing a
material (4) having a refractive index that can vary under the
action of the electrical and/or magnetic and/or electromagnetic
signal generated during a movement of the eye.
Inventors: |
Michel; Francois (Thonon les
Balns, FR), Buisine; Jean-Marc (Louvil,
FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Michel; Francois
Buisine; Jean-Marc |
Thonon les Balns
Louvil |
N/A
N/A |
FR
FR |
|
|
Assignee: |
Centre National de la Recherche
Scientifique--CNRS (Paris, FR)
Michel; Francois (Thonon-les-Bains, FR)
|
Family
ID: |
38009752 |
Appl.
No.: |
12/529,243 |
Filed: |
February 8, 2008 |
PCT
Filed: |
February 08, 2008 |
PCT No.: |
PCT/FR2008/000160 |
371(c)(1),(2),(4) Date: |
December 02, 2009 |
PCT
Pub. No.: |
WO2008/119894 |
PCT
Pub. Date: |
October 09, 2008 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20100121443 A1 |
May 13, 2010 |
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Foreign Application Priority Data
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|
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Mar 1, 2007 [FR] |
|
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07 53575 |
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Current U.S.
Class: |
623/6.22;
623/6.37 |
Current CPC
Class: |
A61F
2/1627 (20130101); A61F 2250/0001 (20130101); A61F
2250/0002 (20130101); A61F 2210/009 (20130101) |
Current International
Class: |
A61F
2/16 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
2 777 091 |
|
Oct 1999 |
|
FR |
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WO 85/05466 |
|
Dec 1985 |
|
WO |
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WO 94/23334 |
|
Oct 1994 |
|
WO |
|
WO 03/007851 |
|
Jan 2003 |
|
WO |
|
Primary Examiner: Willse; David H
Assistant Examiner: Shipmon; Tiffany
Attorney, Agent or Firm: Arent Fox LLP
Claims
The invention claimed is:
1. A device for the vision correction of an eye including: a
converter generating an electrical and/or magnetic and/or
electromagnetic signal solely from mechanical energy generated by a
movement by the eye; a soft lens intended to be aligned with the
eye, the converter being positioned in relation to the lens such
that the electrical and/or the magnetic and/or the electromagnetic
signal generated during the movement of the eye cause the optical
properties of the lens to change, wherein the lens includes a
polymer material containing a material having a refractive index
that can vary under the action of the electrical and/or magnetic
and/or electromagnetic signal generated solely from the
converter.
2. A device according to claim 1, wherein the material includes
liquid crystals having an orientation liable to vary under the
action of the voltage of the electrical and/or magnetic and/or
electromagnetic signal during the movement of the eye.
3. A device according to claim 2, wherein the converter is arranged
such that the threshold effect of the modification of the
orientation of the liquid crystals is reached when an accommodation
movement of the eyes starts at the punctum remotum.
4. A device according to claim 2, wherein the converter is arranged
such that the threshold effect of the modification of the
orientation of the liquid crystals is reached when the optical axes
of both eyes intersect at a distance of approximately five meters
in relation to the eyes.
5. A device according to claim 2 wherein the converter includes a
pair of electrodes which are transparent in the visible region,
with the electrodes of the pair of electrodes being positioned on
either side of the lens.
6. A device according to claim 5, wherein the electrodes of the
pair of electrodes include a mixed indium/tin oxide material.
7. A device according to claim 5, wherein the electrodes of the
pair of electrodes include a conducting polymer material.
8. A device according to claim 2 wherein the converter includes a
pressure sensor, a transducer able to transform a pressure
resulting from the movement of the eye into an electrical and/or
magnetic and/or electromagnetic signal.
9. A device according to claim 1 or 2, wherein the lens includes a
composite of the polymer material and liquid crystals.
10. A device according to claim 9, wherein the composite is a
polymer matrix swollen with liquid crystals.
11. A device according to claim 9, wherein the composite is a
polymer and liquid crystals gel.
12. A device according to claim 11, wherein the polymer is a
polyacrylate having an optical index substantially equal to the
average optical index of the liquid crystals.
13. A device according to claim 9, wherein the composite is a
polymer matrix including a dispersion of liquid crystal
droplets.
14. A device according to claim 9, wherein the liquid crystal are
nematic liquid crystals.
15. A device according to claim 9, wherein the liquid crystals are
ferroelectric liquid crystals.
16. A device according to claim 9, wherein the liquid crystals have
a negative dielectric anisotropy and a homeotropic orientation in
the absence of an electrical field.
17. A device according to claim 9, wherein the liquid crystals have
a positive dielectric anisotropy and have a planar orientation in
the absence of an electrical field.
18. A device according to claim 9, wherein the liquid crystals are
inclined in relation to an homeotrope orientation in the absence of
an electromagnetic field.
19. A device according to claim 9, wherein the liquid crystals have
an orientation liable to vary under the action of the voltage of
the electrical and/or magnetic and/or electromagnetic signal during
the convergence movement of both eyes.
Description
The invention relates to a device for the vision correction of an
eye including: a converter which can generate an electrical and/or
magnetic and/or electromagnetic signal in response to the
mechanical energy generated by a movement of the eye; a soft lens
arranged so as to be aligned with the eye,
the converter being positioned in relation to the lens such that
the electrical and/or magnetic and/or electromagnetic generated
during the movement of the eye causes the optical properties of the
lens to change.
For a converter capable of generating an electrical signal, such a
device is described in the international application WO
2004/004605. This document relates to a device of the ocular
implant type wherein the soft lens is an intraocular lens which can
be implanted in the patient's eye, for example when the patient
suffers from cataract. In this document, a converter makes it
possible to transform the mechanical energy which is generated by
the movement of an eye into an electrical signal. This converter
more particularly includes pressure sensors which detect the
convergence movement of the eyes. This electrical signal is then
supplied to the lens in the form of a detector voltage. Under the
effect of such electrical voltage, the radius of curvature of the
length undergoes a modification because of the piezoelectric
effect. This modification is caused by a open loop wire movable
under the effect of an electrical voltage which surrounds the lens
and thus modifies the radius of curvature thereof when a voltage is
applied. Such a device is pseudo-accommodative in the meaning that
accommodation is carried out as a reaction to the movement of both
eyes, when the eyes converge upon the passage from a far vision to
a near vision. The effect of the modification of the curvature is
then performed when this convergence condition is detected.
In the above-mentioned application, the movement generating a
modification of the optical properties of the lens is a particular
movement of both eyes corresponding to a convergence. However,
within the scope of the invention, the movement of the eye can be
any movement, for example defined by a variation in the orientation
in space of the optical axis of an eye. Particular properties of
elements of the invention can then be defined as a function of a
particular movement. Such a device has the important advantage that
the mechanical energy related to the movement of the eyes is
transformed into an electrical energy liable to be used for
modifying the optical properties of the lens through a
piezoelectric effect. Using mechanical energy as a source of
initial energy more particularly in the form of a pressure, or of a
variation in length or of a deformation has the advantage of not
being related to the user's age. As a matter of fact, whatever his
or her age, the movement of the eye is the same to converge.
Although it is advantageous for generating a pseudo-accommodative
implant for the vision correction, such a device however has some
disadvantages.
More particularly, it is difficult to modify the curvature of an
intra-ocular lens since the latter is polluted by fibrotic
deposits. The lens thus sticks to the fabrics on which it is placed
which makes it impossible to modify the curvature in a controlled
and satisfactory way reproducible over time.
In addition, in the above-mentioned international application, the
structure and the composition of the lens are adapted so that the
curvature can be modified as a response to the movement of the
eyes. This composition is then no longer adapted for other types of
modification of the optical properties of the lens.
In addition, it is known that, within the scope of an intra-ocular
lens, the best way to insert the lens is to fold it, to insert it
into a small size cut in the eye and to let the lens go back to a
desired shape. Because of the means used for modifying the
curvature in the above-mentioned international application, such a
procedure is more complex.
The invention more particularly aims at remedying such
drawbacks.
A problem solved by the invention thus consists in providing a
device for the vision correction such as previously described,
which can react to the mechanical energy generated by a movement of
the eye and for which the modifications in the optical properties
of the lens are simplified and better controlled. It is also
suitable that the properties of the lens are stable in the absence
of all electrical and/or magnetic and/or electromagnetic
signals.
Document WO-A-03/007851 is also known, which discloses a device
such as mentioned above.
In this document, liquid crystals are inserted into a bag to form
the soft lens. Under the action of a contraction of the iris, the
orientation of the liquid crystals can be modified so that the
optical properties of the lens change.
However, the nature of the bag or the lens is not mentioned in this
document.
Now, as mentioned above, within the scope of an intra-ocular lens,
the best way to insert the lens consists in folding it, and
inserting it into a small size cut in the eye and to let the lens
go back to a desired shape. Now, if any bag including liquid
crystals was used, this folding would cause a modification in the
molecular arrangement of the liquid crystals. This modification can
then be irreversible thus making the device unserviceable.
Further to the above-mentioned document, the invention thus aims at
improving the soft lens.
Such problems are solved by a device for the vision correction of
an eye such as previously described and characterised in that the
soft lens includes a polymer material in which a material having a
refraction index liable to vary under the action of the electrical
and/or magnetic and/or electromagnetic signal in response to the
movement of the eye is included.
Thanks to such a device, during the movements of the eye, the
refraction index of the material can vary simply under the action
of the electrical and/or magnetic and/or electromagnetic signal
which modifies the optical properties of the lens. The device is
thus liable to adapt in reaction to the movements of the eye. The
insertion of the material having a variable refraction index into
the polymer makes it possible to obtain this modification in an
adapted way in response to a movement of the eye. As a matter of
fact, it is possible to obtain some stability of the material
having a variable index in the polymer in the absence of the
electrical and/or magnetic and/or electromagnetic signal, while
having a correct reactivity of the material to the signal applied
in case of a movement of the eye.
According to the invention, the curvature of the lens is not
necessarily modified, which makes it possible to avoid the
above-mentioned problems related to the fibrosis of the fabrics in
contact with the lens. The fact that the material having a variable
refraction index is in the lens enables a simple control of the
properties of modifying the lens, since the outside environment of
the lens, such as the fibroses, does not influence the modification
in the optical properties.
In the field of intra-ocular lens with a variable optical power,
the American patient U.S. Pat. No. 4,373,218 is also known. Such
patent teaches a device for the vision correction of an eye
including a lens, the lens including liquid crystals. Such liquid
crystals have the known property of orientating under the effect of
an electrical or magnetic or electromagnetic field. In the
above-mentioned patent, according to one embodiment, electrodes are
placed in the user's eye thus making it possible to detect an
accommodation. However, in this patent, it is not the mechanical
energy related to the movement of the eyes which is detected but an
electrical potential generated by the muscles during the
accommodation. The utilisation of the energy generated by the
muscles during the accommodation is not sufficient since it is not
stable and more particularly varies with the user's age, which will
thus require a regular modification of the device. In addition, in
the above-mentioned patent, the embodiment only uses the effect of
an electrical field. However, within the scope of the invention,
the used effects can be electrical and/or magnetic and/or
electromagnetic.
In addition, the liquid crystals described in the above-mentioned
patent are not adapted to react satisfactorily in response to a
movement of the eye. As a matter of fact, they are not soaking in a
medium allowing both a good orientation stability and a correct
homogeneity in space and time in the absence of an electromagnetic
field, and a correct spatial reaction and a correct homogeneity in
presence of an electrical field. On the contrary, in the invention,
positioning the material having a variable index in a polymer
material makes it possible to gain this advantage. In addition, the
invention makes it possible to gain this advantage in the presence
of electrical and/or magnetic and/or electromagnetic fields.
In this patent, this is not the mechanical energy related to the
movement of an eye which generates the electrical signal required
for modifying the optical properties of the liquid crystals. This
patent thus uses no converter. Because of the utilisation of the
electrical potentials only generated by the muscle zones of the
eyes, the device described in this patent is thus not satisfactory
in practice.
The above-mentioned patent thus does not solve the above-mentioned
problem related to the required modification as a reaction to a
movement of the eye.
In addition, in the above-mentioned patent, it is difficult to give
a desired shape to the lens. On the contrary, using a polymer
material which can be used as a matrix makes it possible to impart
such a shape in a simple way, more particularly through the
construction of composite plates to be cut and to be machined. In
addition, according to the invention, it is possible to provide a
pre-defined orientation to the liquid crystals as soon as the lens
is manufactured and not only when the lens is placed in the eye.
Eventually, the lens according to the invention makes it possible,
thanks to the utilisation of a polymer matrix including the
material having a variable index, for example in the form of liquid
crystals, to keep a satisfactory orientation of the liquid crystals
even though the lens must be folded or handled prior to being
introduced into the user's eye.
The application for a patent EP-A-1 068 555 is also known, wherein
a device is described for the vision correction of an eye including
a lens, including liquid crystals. Liquid crystals have the known
property of orientating under the effect of a stress field. In this
application, the material used for manufacturing the lens includes
a three-dimension liquid crystal polymer. Now, in such a liquid
crystal polymer, the crystalline liquid parts of the molecules are
strictly frozen, so that the orientation effect of the crystalline
liquid parts is obtained only when a high stress is exerted on the
whole polymer. This is the reason why, in the present application,
the modification or the orientation is provided under the action of
a mechanical stress, for example during a blinking of the eyelid.
Liquid crystal polymers described in the present application are
thus not liable to orientate under the action of an electrical
and/or magnetic and/or electromagnetic signal and more particularly
they are not liable to orientate under the action of the electrical
and/or magnetic and/or electromagnetic signal generated by the
movement of the eye.
Now, other advantageous characteristics of the invention will be
described.
When the signal generated by the converter following the movement
of the eye is electrical, it can correspond to the relatively low
voltage, typically of the order of 1 volt to 5, volts. Thus, it is
advantageous that the effect of the reaction to the movement of the
eye occurs even when the voltage generated by the movement of the
eye is low. Only low voltages are compatible with the human
body.
This additional advantage is reached according to one embodiment of
the invention through the characteristic according to which the
material includes liquid crystals having an orientation liable to
vary under the action of an electrical and/or magnetic and/or
electromagnetic signal during the movement of the eye.
According to this embodiment, further to the movement of the eye,
the mechanical signal may generate an electrical and/or magnetic
and/or electromagnetic signal and the liquid crystals orientate
under the action of the electrical and/or magnetic and/or
electromagnetic fields associated thereto, which results in the
modification in the refraction index of the lens. The lens thus
behaves like a birefringent material which reacts to the movements
of the eye.
In addition, the liquid crystals have the property of easily
orientating under the action of an even low electrical voltage,
typically of the order of one volt. For applications to an
intra-ocular implant, such a device thus makes it possible to use
the low voltages generated by the movement of the eye.
Advantageously, the lens includes a composite of the polymer
material and the liquid crystals. Thanks to this composite, the
lens can be easily handled without irreversibly modifying the
molecular arrangement of the liquid crystals which would make the
device unserviceable.
According to one embodiment, the composite is a polymer matrix
swollen with liquid crystals. Such an embodiment has the advantage
of being easily produced. A polymer protection envelope can also be
added which is aimed at protecting the liquid crystals of the
polymer matrix so as to prevent them from escaping from the polymer
matrix.
According to another embodiment, the composite is a polymer and
liquid crystals gel. This embodiment has the advantage of allowing
an easy change in the orientation of the liquid crystals for
relatively low pressure voltages compatible with the energy
generated by the movement of the eye. In a polymer gel, the
movement of the liquid crystals is facilitated. As already
mentioned, a polymer protection envelope can also be added.
According to still another embodiment of the invention, the
composite is a polymer matrix including a dispersion of liquid
crystal droplets. The droplets can be micro-droplets or
nano-droplets. This embodiment has the advantage of being able to
present an optical diffusion of the lens compatible with the
considered applications. This embodiment also has the advantage
that the electrical voltage to be applied to cause the orientation
of the liquid crystals to change is relatively low and compatible
with the energy generated by the movement of the eye.
In such three embodiments, the fact that the liquid crystals are
associated with the polymer in the form of a composite has the
advantage of allowing a flexibility of the lens which thus makes it
possible to fold it to introduce it into the eye in the case of
intra-ocular lens, so that the required cut in a patient's eye is
relatively small. The shape memory properties of the polymer then
enable the lens to go back to its useful shape, which substantially
corresponds to a crystalline further to the folding and
introduction of the lens.
In addition, according to the invention, the liquid crystals can be
either nematic liquid crystals having the advantage of being the
most currently known crystals and thus enabling a simple
embodiment, or ferroelectric liquid crystals which have the
advantage of having a correct electrical response and thus a better
reaction to the voltage applied, even though the latter is
relatively low, during the movement of the eye.
The polymer associated with the liquid crystals in the lens can be
a polyacrylate having an optical index n.sub.poly substantially
equal to the average optical index of the liquid crystals n.sub.CL,
so as to prevent diffusion phenomena within the lens.
Now, other advantageous characteristics of the transparent
electrodes according to the invention will be described according
to the particular embodiment of the invention described
here-above.
According to one embodiment of such electrodes, these include a
mixed indium/tin oxide material known as ITO. This material has the
advantage of being a conducting and usually transparent
material.
According to one embodiment of such electrodes, these include a
conducting polymer. The advantage of such conducting polymers is
that they have a good biological compatibility and can thus be
easily used more particularly in the case of an intra-ocular
device. This conducting polymer also has the advantage of being
usable as a protection envelope of the lens associated with the
liquid crystals to keep the crystals in the polymer.
In addition, in the embodiments wherein a voltage is applied to the
liquid crystals, so as to modify their orientation, it is
advantageous that the liquid crystals currently change orientation,
for example without a part of the crystals rotating in one
direction and the other part rotating in another direction.
This additional advantage is obtained through the characteristics
according to which liquid crystals are inclined with respect to an
homeotrope orientation in the lens, independently of the
application of any voltage. This inclination corresponds to a
pre-orientation of the liquid crystals and can be obtained through
the application of a pre-orientation of an electrical field during
the manufacturing of the lens and more particularly during the
polymerisation of the lens.
This preferred orientation can also be obtained through particular
chemical treatments of the external surfaces of the lens, for
example through the deposition of molecules inducing a specific
orientation of the molecules of liquid crystals through weak
chemical connections.
In addition, the refraction index of the polymer is substantially
equal to the refraction index of the liquid crystals, so as to
obtain a transparent medium.
In addition, it is also advantageous that the converter can simply
generate a voltage and does not hinder the vision of the user of
the device according to the invention when the latter is placed in
the user's eye.
This additional advantage is reached according to one embodiment of
the invention through the characteristic according to which the
converter includes a pair of electrodes transparent in the visible
region, the electrodes of the pair of electrodes being positioned
on either side of the lens.
So, the electrodes form a capacitor around the lens. The capacitor
makes it possible to apply the voltage to the material having a
variable refraction index, so as to vary the refraction index
during the movement of the eye. The fact that the electrodes are
transparent in the visible region further makes it possible not to
hinder the vision of the user of the device.
In addition, in order to provide a device whose response to the
movement of the eye is satisfactory, so as to correctly modify the
optical properties of the lens, the converter may include a
pressure sensor and a transducer capable of transforming a pressure
into an electrical and/or magnetic and/or electromagnetic signal.
Thus, when the eye moves, the pressure generated by such movement
is detected by the pressure sensor and the transducer will then
generate the electrical and/or magnetic and/or electromagnetic
signal. More generally, the converter may include means for
detecting the mechanical energy caused by a rotation of one eye or
both eyes.
The converter also preferably includes a computer so as to adapt
the electrical and/or magnetic and/or electromagnetic signal
generated as a function of the detected mechanical energy, and more
particularly pressure. The pressure sensors and the computer
preferably communicate through ultrasound.
In addition, in the case of an accommodation movement of a user's
eyes corresponding to a convergence of the eyes, it is advantageous
that the optical properties of the lens are not modified out of the
accommodation path, but start from a point called punctum remotum
corresponding to the point from which a sound eye starts
accommodating. Thus, the accommodating simulation effect gets much
closer to a real accommodation. This punctum remotum is situated
approximately five meters away from the eyes.
This additional advantage is obtained according to one embodiment
of the invention through the characteristic according to which the
converter is so arranged that the threshold electrical voltage for
the modification of the orientation of the liquid crystals is
reached when a movement of accommodation of the eyes starts at the
punctum remotum.
As a matter of fact, it is known that for liquid crystals, the
effect of the modification of the orientation starts only from a
threshold electrical voltage for the modification of the
orientation. From this threshold voltage, the crystals start to
orientate their dipolar moment. For liquid crystals in a thin film,
beyond this threshold voltage, the variation of the orientation of
the liquid crystals is then substantially proportional to the
applied electrical voltage. This effect is known as a Freedericksz
effect.
Using this threshold voltage effect, the converter is then arranged
so that the orientation effect starts only when the movement of the
eyes reaches the punctum remotum. This makes it possible to obtain
a good simulation of the accommodation during the movement of
accommodation of the eyes corresponding to a convergence. This
advantage is more particularly reached because the electrical
and/or magnetic and/or electromagnetic signal generated results
from the mechanical energy due to the convergence of the eyes,
which makes it possible to adapt the signal as a function of this
movement.
On an average, the punctum remotum is located approximately five
meters away from the eyes. Thus, the converter can be so arranged
that the threshold voltage for the modification of the orientation
of the liquid crystals is reached when the optical axes of both
eyes intersect at a distance of approximately five meters with
respect to the eyes.
This particular arrangement of the converter can be obtained by
programming the above-mentioned computer so as to reach this
result. This result is also reached through the appropriate
selection of materials, more particularly for the soft lens.
The invention also relates to a soft lens including a polymer
material in which a material having a refraction index likely to
vary under the action of an electrical and/or magnetic and/or
electromagnetic signal liable to be produced through the
transformation of the mechanical energy produced during the
movement of an eye, is included.
All the characteristics described here-above as relating to the
lens in the device for the vision correction are also applied to
such a lens.
Now, an embodiment of the invention will be described while
referring to the appended drawings wherein:
FIG. 1 shows a device for the vision correction of an eye according
to one embodiment of the invention;
FIG. 2 shows a planar orientation of the liquid crystals in the
lens according to the invention;
FIG. 3 shows a homeotrope orientation of the liquid crystals in the
lens according to the invention;
FIG. 4 is a curve showing the variation in the orientation of the
liquid crystals as a function of the voltage to the lens according
to the invention;
FIG. 5 shows four situations of a user's eyes which can activate or
not the generation of an electrical signal, further to the
detection of the movement of the eyes.
In FIG. 1, a device 1 for the vision correction of an eye 6
includes a lens 2. The lens 2 includes liquid crystals 4 in a
polymer 7. The lens 2 is surrounded on both sides by transparent
electrodes 5A and 5B. The muscle tissues of the eye 6 are connected
to a converter 3 including means 3A for detecting the movement of
the eye 6 and means 3B for generating an electrical signal as a
response to such movement of the eye. The means 3A for example
include pressure sensors.
The converter 3 including the means 3A for detecting a movement of
the eye 6 and generating an electrical signal as a response to this
movement can be as described in the international application WO
2004/004605. In particular, as described in this document, the
converters 3 may include one or several strain gages which can be
made from miniature absolute pressure sensors 3A, which are
inserted under the insertion tendon of the external rectus muscles.
This can be millimetric microstructures on silicon, which are
supplied without any contact and without any battery, like through
induction. Such systems include a sensitive element, a converter
and a coupler associated to a secondary antenna enabling the remote
supply of the system and the remote transmission of the pressure
measurement.
More precisely, the sensitive element is a mechanical
microstructure which is deformed under the effect of a force, i.e.
the pressure it is submitted to, a deformation which causes the
modification of capacities integrated in the sensitive assembly.
The electrical value of the variations in capacities is transformed
into a digital signal through the converter. The sensitive element
may also show shape variations or axial deformations such as
extensions or compressions.
Thanks to the converter 3 as described here-above, it is thus
possible to obtain, in response to a movement of the eye, an
electrical signal corresponding to the voltage between the
transparent electrodes 5A and 5B of approximately 1, to 5, volts.
The generated electrical tension depends on the movement of the
eye, such movement being the movement of an eye or a combined
movement of both eyes. In the example described, the converter 3 is
a transducer which transforms the mechanical energy caused by the
movement of an eye into an electrical signal. Other embodiments of
this converter can be considered, so long as an electrical
and/magnetic and/or electromagnetic signal is generated in response
to a movement of the eye.
Now, the lens 2 and the liquid crystals 4 associated within the
scope of an accommodation corresponding to a convergence of the
eyes will now be described in greater details.
The lens 2 is a symmetrical biconvex lens having a convergence C
close to 21 dioptres for 1 emmetrope eye, with an average
refraction index n equal to 1.5 and a radius of curvature R. For a
biconvex lens 2, it is known that the convergence is given by the
relation C=2(n-1)/R, so that the curvature is in this case 5
centimeters. The diameter of the lens 2 is L=6 millimeters, and the
radius of curvature is 50 millimeters. The thickness of the lens of
the order of 180 micrometers can be deduced therefrom.
In this case, if it is desired that the convergence varies by
approximately 3 dioptres during the adjustment of the lens, we have
.DELTA.C=(2..DELTA.)/R=3 dioptres, i.e. .DELTA.n=0.0075.
According to this example, the liquid crystals must thus be capable
of modifying the refraction index having a value equal to
.DELTA.n=0.0075,, which is possible, since if n.sub.e and n.sub.o
are respectively the extraordinary and ordinary indexes of the
liquid crystals we have:
0.05<n.sub.e-n.sub.o-.DELTA.n<0.25
According to the invention, the liquid crystals have ordinary and
extraordinary indexes which are respectively equal to 1.5 and
1.65.
According to the orientation of the liquid crystal molecules in the
lens, it is known that the apparent index of the medium comprising
the liquid crystal varies.
For a planar orientation wherein the molecules are parallel to the
lower and upper substrates composing the internal surface of the
lens, for a natural and non-polarised light, it is known that the
apparent index is equal to:
N.sub.p=[(n.sub.o.sup.2+n.sub.e.sup.2)/3].sup.1/2=1.5767
This planar orientation is schematically represented in FIG. 2. The
liquid crystals 4 are positioned parallel to the surfaces 2A and 2B
of the lens 2.
For an homeotropic orientation wherein the molecules are
perpendicular to the lower and upper substrates composing the
internal surface of the lens, for a natural and non-polarised
light, it is known that the apparent index is equal to:
n.sub.p=n.sub.o=1.65
This homeotropic orientation is schematically represented in FIG.
3. The liquid crystals 4 are positioned perpendicularly to the
surfaces 2A and 2B of the lens 2.
During a change in the orientation of the liquid crystals under the
effect of a voltage during a movement of the eye, the liquid
crystals can change from a homeotropic orientation to a planar
orientation.
In this case, the maximum variation of the index is
n.sub.p-n.sub.o=0.0767 which is thus perfectly acceptable to
perform a change in convergence by 3 dioptres, as mentioned
above.
More precisely, according to one embodiment of the invention, it is
desired for the device according to the invention to make it
possible to increase the convergence, with a constant radius of
curvature, by switching from a far vision to a near vision. The
arrangement of the liquid crystals in the lens is then adapted to
reach this result.
For this purpose, it is necessary for the lens 2 to have a low
index for a far vision, thus for the liquid crystal molecules to
have a homeotropic orientation and a high index for a near vision,
thus for the liquid crystal molecules to have a planar orientation
since, as mentioned above, n.sub.p is greater than n.sub.o.
In addition, the dielectric anisotropy of the liquid crystal
molecules for two orthogonal positions of an electrical field as
.DELTA..epsilon., with: .DELTA..epsilon.>0 if the dipolar moment
is directed along the main direction of the extension of molecules;
.DELTA..epsilon.<0 if the dipolar moment is orientated
perpendicularly to the main direction of the molecules
extension.
To have a positive variation of the index through the switching of
the molecules to a planar orientation under the effect of an
electrical field, a liquid crystal with a negative dielectric
anisotropy and a homeotropic orientation is selected in the absence
of a field. The converter 3 is then arranged so that the eye is at
rest in a far vision and that no electrical field is supplied to
the liquid crystal in a far vision.
In order to have a positive variation of the index through the
switching of the molecules to a homeotropic orientation under the
effect of an electrical field, a liquid crystal with a positive
dielectric anisotropy and a planar orientation is selected in the
absence of a field.
In order to guarantee that the orientation of the liquid crystal
molecules is homeotropic on the whole thickness of the liquid
crystal, the surfaces limiting the lens in a way known per se are
treated, for example in the field of liquid crystal display
devices.
A pre-orientation of the liquid crystals can thus be obtained by
applying an electrical pre-orientation field during the
manufacturing of the lens and more particularly during the
polymerisation of the lens.
The same surface treatment procedures and the application of an
electrical pre-orientation field are applicable to guarantee a
planar orientation of the molecules on the whole thickness of the
lens.
The effect of the voltage applied to the liquid crystals is then an
orientation of the dipolar moment of the liquid crystals
perpendicularly to the surfaces limiting the liquid crystals. To
obtain a homogenous orientation in the presence of the electrical
field, a pre-orientation is imparted to the molecules in the
absence of a field. The liquid crystals are thus slightly inclined
with respect to the homeotropic position.
The liquid crystals used can be nematic liquid crystals, or
ferroelectric liquid crystals. Depending on the type of liquid
crystals selected, the conditions of the orientation may vary more
particularly as a function of the dielectric anisotropy
.DELTA..epsilon..
Now the curve of the response of the liquid crystals as a function
of the voltage applied in the lens in now described while referring
to FIG. 4. This curve is known per se within the scope of the
Freedericks effect. The threshold of V.sub.o is given by the
following expression for a thin film corresponding to the thickness
of the lens:
V.sub.o=.PI.(K/.DELTA..epsilon.) with K being the elasticity
constant of the liquid crystal.
Beyond this threshold voltage, the angle .alpha. giving the
alignment orientation of the liquid crystals molecules with the
surface of the lens 2 is proportional to the electrical field
applied, still with a thin film.
As the thickness of the lens is approximately 180 micrometers, the
thin film condition is satisfied.
For a conventional liquid crystal, the preceding formula gives a
threshold voltage of approximately 1 volt and a maximum voltage to
obtain a planar orientation of the order of 3 volts.
These voltages are compatible with the electrical energy which can
be generated by the converter 3 further to the movement of the eye
or the eyes.
Thus, during the approaching between the far vision and the near
vision, the index of the lens is not modified. This characteristic
corresponds to the situation for a sound crystalline which makes no
accommodation before the convergence point of the eyes reaches the
distance of approximately 5 meters. This point of the starting of
the accommodation is called punctum remotum.
The converter is then arranged so that, when the eyes reach such a
5 meter convergence, the electrical signal generated by the
converter corresponds to the voltage equal to the threshold voltage
V.sub.o. The modification of the orientation is then linear when
the eyes converge further.
An exemplary embodiment of the lens 2 associated with the liquid
crystals 4 will now be described in greater details.
Generally, the lens 2 includes a composite of a polymer material 7
and liquid crystals 4. Thanks to this composite, the lens can be
easily handled without irreversibly modifying the molecular
arrangement of the liquid crystals which would make the device
unserviceable.
This lens 2 is for example a polymer matrix 7 having a biconvex
shape formed by liquid crystal 4. A protection envelope also made
of polymer possibly protects this polymer matrix. The polymer used
is a polyacrylate having an optical index n.sub.poly which is
substantially equal to the average optical index of the liquid
crystals n.sub.CL so as to prevent diffusion phenomena within the
lens.
According to a first alternative solution, the lens 2 also includes
a polymer 7 and liquid crystal gel 4. The liquid crystals 4 are
then frozen in the polymer network while being easily movable under
the action of the electrical field.
According to a second alternative solution, the lens 2 can also
include droplets of liquid crystals 4 in a polymer matrix 7. In
this case, the liquid crystals 4 are preferably of a ferroelectric
type. The insertion of polymer droplets in a polymer matrix is
known per se. The manufacturing method of such a structure is for
example disclosed in the work by [M. BOUSSOUALEM (doctoral thesis
of Universite du Littoral Cote d'Opale December 2005) "Contribution
a l'optimisation de la qualite de regulation lumineuse de films
composites: etude physicochimique aux interfaces matrice-phase
complexe"; M. BOUSSOUALEN, M. ISMAILI, J.-F. LAMONOER, J. M.
BUISINE, F. ROUSSEL Polarization field-effect at liquid Crystal
droplets-polymer interface Physical Review 73 (2006)].
In all these embodiments, the liquid crystals 4 are included in a
polymer material 7, so as to have a good reactivity to the
electrical field, while being relatively stable in the absence of
an electrical field.
In all these embodiments and more particularly when the lens is
used as an intra-ocular implant, it can include an optical part
from where arms also called haptic arms protrude, which are used
for fixing the implant in the patient's eye.
Now, the electrodes 5A and 5B will be described in greater details.
Such electrodes 5A and 5B are transparent electrodes made of a
mixed indium/tin oxide material. They are positioned so as to
follow the shape of the surfaces of the lens 2 and are thus
concave. They are positioned in relation to the lens 2 so as to
apply a voltage in the area of the lens 2 which includes the liquid
crystals.
According to an alternative solution, such electrodes 5A and 5B
include a conducting polymer.
Now, the device 1 according to the invention will be described in
operation.
Further to surgery, the lens 2 is positioned in the eye for example
as an intra-ocular implant, in the case of cataract surgery. The
converter 3 is connected to the muscles of the eye to detect a
movement of the eye and generate an electrical signal in response.
This electrical signal can be supplied to the lens 2, as a voltage,
through the electrodes 5A and 5B.
When the bearer of the device 1 has a movement of the eye for
example a convergence movement of both eyes corresponding to the
switching from a far vision to a near vision, the converter 3
detects this movement through the sensor 3A. When this movement is
detected, an electrical signal is generated by the generation means
3B. This electrical signal is supplied to the electrodes 5A and 5B
so that a voltage is generated between the electrodes 5A and
5B.
According to the value of this voltage and depending on the graph
of the response, as illustrated in FIG. 4, the orientation of the
liquid crystals 4 is modified. As previously described, these
liquid crystals can be selected so that the apparent index of the
lens 2 increases in the case of convergence of the user's eyes.
When the index has increased, the user has a correct near vision,
which does not require lenses.
Now, alternative solutions to the invention will be described.
The fact that the electrical signal is supplied to the lens as a
voltage so as to modify the orientation of the liquid crystals has
been described. However, it is also possible that the liquid
crystals are orientated under the effect of the magnetic field
which will then entail a modification of the refraction index of
the lens, as mentioned above. This effect, which is similar to the
above-mentioned Freedericks effect, is known. To generate the
magnetic field, electromagnetic transducers can be used on the
muscles of the eye and apply a magnetic field generated by the
movement of the eye to the lens. This embodiment has the advantage
of not requiring electrodes at the lens.
In addition, the device has been described within the scope of a
particular movement of the eyes corresponding to the switching of a
far vision to a near vision. It should be noted that the converter
can detect any movement of one eye or both eyes and generate the
electrical signal as a function of this movement. While referring
to FIG. 5, the converter can be arranged so that the electrical
signal is for example generated in the case "d" for both eyes, in
the cases "b and c" for the eye in convergence alone and for none
of the eyes in the case "a".
In addition, an embodiment in which the lens 2 is used as an
intra-ocular implant has been described. As an alternative
solution, the lens 2 can also be a contact lens or an ocular glass.
In the latter case, it is sufficient to connect the ocular glass to
the muscles of the eye or of both eyes and to detect the movement
of the eye or of the eyes using the converter. Thanks to the
converter according to the invention, the movement of the eyes can
then be converted into an electrical signal which can modify the
optical index of the ocular glass.
* * * * *